There is a very rapid development of original systems that can be remotely controlled or addressed by playing with chemical and physical concepts. Here, we present the synergetic combination of external magnetic and electric fields to promote, in a double contactless mode, the rotational motion and the concomitant generation of light-emission at the level of a gold-coated iron wire. The latter can be moved by rotating magnetic fields. Simultaneously, an electric field induces its remote polarization, which triggers the local generation of electrochemiluminescence (ECL) by bipolar electrochemistry. During rotation, the motion is tracked by changes in ECL intensity as a function of the orientation of the conducting wire in the electric field. The ECL behavior of the rotating bipolar wire is rationalized by considering the angular dependence of the polarization. Unlike previously reported systems, the rotation induces enhanced ECL emission due to the convective flow produced by the motion. This demonstrates that ECL emission can be coupled to magnetically-controlled rotating bipolar objects. Such dual magnetically- and electrically addressable dynamic systems open exciting perspectives for integrating new functions such as imaging and sensing capabilities.
Y. Zhao, J. Yu, G. Xu, N. Sojic, G. Loget
We introduce the photo-induced electrochemiluminescence (P-ECL) of the model ECL system involving the simultaneous oxidation of [Ru(bpy)3]2+ and tri-n-propylamine (TPrA). This system classically requires highly anodic potentials, >+1 V vs SCE for ECL generation. In the reported approach, the ECL emission is triggered by holes (h+) photogenerated in an n-type semiconductor (SC) electrode, which is normally highly challenging due to competing photocorrosion occurring on SC electrodes in aqueous electrolytes. We employ here Si-based tunnel electrodes protected by a few nm-thick SiOx and Ni stabilizing thin films and demonstrate that this construct allows generating P-ECL in water. This system is based on an upconversion process where light absorption at 810 nm induces ECL emission (635 nm) at a record low electrochemical potential of 0.5 V vs SCE. Neither this excitation wavelength nor this low applied potential is able to stimulate ECL light if applied separately. But their synergetic actions lead to a stable and intense ECL emission in water. This P‑ECL strategy can be extended to other luminophores and is promising for ultrasensitive detection, light-addressable and imaging devices.
A. Perro, L. Giraud, N. Coudon, S. Shanmugathasan, B. Goudeau, J.-P. Douliez and V. Ravaine
Coacervation is a phase separation process involving two aqueous phases, one solute-phase and one solute-poor phase. It is frequently observed among oppositely-charged polyelectrolyte systems. In this study, we focus on self-coacervation involving a single polymer chain and investigate its potential for encapsulation applications. Negatively charged polyacrylic acid polymer chains were partially cationized using diamine and carbodiimide chemistry affording ampholytes, named PAA-DA, with tunable charge ratio. When dispersed in water, at pH 7, PAA-DA was soluble but a phase separation occurs when decreasing pH close to the isoelectric point. Coacervation is found only for a given amine-to-acid ratio otherwise precipitation is observed. Increasing the pH above 4 yielded progressive destruction of the coacervates droplets via the formation of vacuoles within droplets and subsequent full homogeneous redispersion of PAA-DA in water. However, addition of calcium allowed increasing the coacervate droplet stability upon increasing the pH to 7 as the divalent ion induced gelation within droplets. Moreover, the coacervate droplets present the ability to spontaneously sequestrate a broad panel of entities, from small molecules to macromolecules or colloids, with different charges, size and hydrophobicity. Thanks to the reversible character of the coacervates, triggered-release could be easily achieved, either by varying the pH or by removing calcium ions in the case of calcium-stabilized coacervates. Self-coacervation presents the advantage of pathway-independent preparation, offering a real output interest in pharmacy, water treatment, food science or diagnostics.
L. Zhang, C. Carucci, S. Reculusa, B. Goudeau, P. Lefrançois, S. Gounel, N. Mano, A. Kuhn
The immobilization of bilirubin oxidase (BOD) on macroporous gold electrodes for the optimization of bioelectrocatalytic activity is described. A bilirubin oxidase mutant S362C (cys‐BOD) engineered with a cysteine residue located on purpose at the enzyme surface close to the T1 active center was used. It allows the attachment in one‐step of a self‐assembled monolayer of the enzyme to gold through a reaction between the thiol group of the cysteine residue and the metal surface. BOD immobilization of wild type and S362C mutant in macroporous gold electrodes allowed high retention of activity and perfect control of the overall BOD loading due to the fine‐tuning of the macroporous structure. The macroporous arrangement together with the use of cys‐BOD makes these rationally designed enzyme‐modified electrodes very promising candidates for high‐performance bioelectrocatalytic devices with improved activity and stability.
M.-C. Tatry, E. Laurichesse, A. Perro, V. Ravaine and V. Schmitt
The aim of the paper is to examine the adsorption kinetics of soft microgels and to understand the role off undamental parameters such as electrostatics and deformability on the process. This knowledge is further exploited to produce microgel-stabilized emulsions using a co-flow microfluidic device.Uncharged microgels made of poly(N-isopropylacrylamide) are synthesized with variable cross-linker contents, and charged ones are produced by introducing pH sensitive co-monomers during the synthesis.The study is carried out by measuring the microgels adsorption kinetics by means of the pendant drop method. The surface pressure is derived from the previous results as a function of time and is measuredas a function of the area compression using a Langmuir trough. Emulsions are produced using a microfluidicdevice varying the microgels concentration and their stability is visually assessed.The microgels deformability as well as higher particle concentrations favour their adsorption. The adsorption is not governed by diffusion, it is cooperative and irreversible. Conversely, the kinetics is slowed down for increasing cross-linking density. The presence of charges slows down the kinetics of adsorption. In the presence of electrolyte, the kinetics accelerates and becomes similar to the one of neutral microgels. The original features of microgel adsorption is highlighted and the differences with adsorption of polymers, star polymers, proteins, and polyelectrolytes are emphasized. Taking benefit from the adsorption kinetics, the required formulation conditions for producing microgel-stabilized emulsions using a co-flow microfluidic device are derived.There exists a critical concentration above which microgels spontaneously adsorb in a sufficient way to decrease the interfacial tension. This critical microgel concentration increases with the cross-linking density and is higher for charged microgels. Whatever the kinetics, the same surface pressure is finally reached. This peculiar behaviour is likely a consequence of the presence of dangling chains in the as-prepared microgels. Consequently, a microgel excess is required to produce emulsions using microfluidics where adsorption has to be spontaneous.
03 September 2019
03 September 2019
01 August 2019